1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a frequency synthesizer or a mixer of high frequency signals, and more particularly, to frequency synthesizing capable of providing a fast operation with a low power consumption by not using a frequency selection switch, but by using mode switching.
2. Description of Related Art
A high speed wireless data transceiving system such as a cellular phone, a digital multimedia broadcasting (DMB) phone, a personal digital assistant (PDA), etc., needs a frequency synthesizer to process multi-tone signals for a frequency down conversion in a transceiver.
FIG. 1 illustrates an example of a conventional frequency synthesizer 100. Referring to FIG. 1, the frequency synthesizer 100 includes a first single side band (SSB) mixer 110, a second SSB mixer 130, and a switch 120 for selecting a frequency. The second SSB mixer 130 generates three frequency signals, such as F13M, F13D and F123, from a first high frequency signal F1 and an output of the switch 120. The first SSB mixer 110 generates a signal F23 from a second high frequency signal F2 and a third high frequency signal F3. In this case, a frequency of the signal F23 is an addition of frequencies of the signals F2 and F3. When the signal F23 is selected by the switch 120, the second SSB mixer 130 generates the signal F123 from the signals F1 and F23, the signal F123 of which a frequency is a difference of frequencies between the signals F1 and F23. Also, when the signal F3 is selected by the switch 120, the second SSB mixer 130 generates the signal F13D from the signals F1 and F3, the signal F13D has a frequency which is a difference of frequencies between the signals F1 and F3. By changing internal wiring of the second SSB mixer 130, the second SSB mixer 130 may generate the signal F13M from the signals F1 and F3, the signal F13M has a frequency which is a sum of frequencies of the signals F1 and F3.
FIG. 2 illustrates another example of a conventional frequency synthesizer 200. Referring to FIG. 2, the frequency synthesizer 200 includes an SSB mixer 210 and a switch 220 for selecting a frequency. The SSB mixer 210 generates a signal F12M from a first high frequency signal F1 and a second high frequency F2, the signal F12M of which a frequency is a sum of frequencies of the signals F1 and F2. By changing internal wiring of the second SSM mixer 210, the SSB mixer 210 may generate a signal F12D from the signals F1 and F2, the signal F12D has a frequency which is a difference of frequencies between the signals F1 and F2. Namely, according to a selection of the switch 220, any one of the signals F12M and F2 may be output. Also, any one of the signals F12D and F2 may be outputted.
As described above, the conventional frequency synthesizer has to generate three multi-frequency signals, for example, 4488, 3960 and 3432 MHz signals, in a transceiver of a system transceiving high speed wireless data. Also, the conventional frequency synthesizer has to use a frequency selection switch to selectively output any one of the generated signals. More mixers may be utilized to output more than three high multi-frequency signals without a frequency selection switch. However, in this case, circuits get more complicated and more power is consumed. Also, when utilizing a frequency selection switch, a large buffer is needed to actuate the switch. Accordingly, power consumption increases. As an example, to implement fast frequency switching of less than 9.5 nsec, and also to output high frequency signals via the switches 120 and 220 illustrated in FIGS. 1 and 2, a larger buffer is needed to be provided in a front portion of the switches 120 and 220.